1. Field of the Invention
The present invention relates to a system for creating a wall for a shaft within a building that will withstand both seismic activity and fire.
2. Description of the Prior Art
It is well known in the building construction industry that elongated shafts within a building, especially vertical shafts, form tunnels through which fire can rapidly spread once a fire starts within the building. Nevertheless, such shafts are absolutely necessary to accommodate elevators, duct work, laundry chutes, and stairwells. Vertical shafts within buildings are necessary for other purposes as well.
Due to the propensity for building shafts to serve as conduits for spreading fire within a building, particular attention must be given to the construction of walls lining the shafts to attempt to make these walls as fireproof as possible. To this end many building codes currently in effect require shafts to be lined with a double thickness of fireproof wallboard. The purpose of requiring this extra thickness is to improve the barriers to the spread of fire so that they will withstand heat and flames for a longer period of time than they would if constructed of a single thickness of fire-resistant wallboard.
While the use of a double thickness of wallboard to line vertical shaft walls does enhance the fire-resistance of a shaft wall across the central, expansive wall surfaces, the mere increase in thickness of a fire-resistant barrier does not address another serious problem of making a shaft wall fire resistant. Specifically, in the construction of conventional walls of elevator shafts and other building shafts, the vertically and horizontally adjacent faces of panels of wallboard forming the surfaces of the shaft meet in abutment with each other. The interstitial crevices between the abutting surfaces are caulked with a conventional caulking material.
A conventional caulking arrangement initially provides a fireproof barrier at the delineations between the abutting wallboard panels. However, conventional caulking does deteriorate significantly over time. Furthermore, this deterioration is greatly accelerated when the building is subjected to seismic activity, such as an earthquake.
During an earthquake abutting wall panels are shaken and move both toward and away from each other and also laterally. This movement has the effect of not only dislodging the caulking, but smashing and grinding it as well. As a consequence, following an earthquake of any significant degree of severity the caulking between the abutting wallboard panels in a building shaft is shaken loose and at least parts of it are highly likely to fall out. As a result, a subsequent fire within the shaft can relatively easily escape the confines of the shaft, despite the double thickness of the wallboard, since it can transverse the shaft lining along paths between the interstitial spaces between abutting wallboard panels. The pressure built up by the expanding gases of combustion aids in forcing the fire through gaps in the caulking.
As major earthquakes in this country and elsewhere have demonstrated, earthquake building codes that were previously thought to be adequate have proven to be very inadequate. As a consequence, earthquake building code requirements have become more and more stringent. At present, in at least some locations in this country, the abutting members facing a vertical shaft, such as an elevator shaft, must be able to withstand cycling within a range of one inch toward and away from each other, and cycling of 0.93 inches laterally relative to each other. Until now there has not been any building shaft wall system that can meet the current cycling requirements for withstanding seismic activity and still maintain integrity as a barrier against the spread of fire following such cycling.
An aggravating factor that promotes the spread of a fire within a building shaft at the seams between abutting wallboard panels is that when a fire is burning within the shaft, it generates a considerable amount of smoke. This smoke is heated and expands, thereby building a substantial pressure within the shaft where the fire is burning. The pressure of smoke from a fire burning within a building shaft literally blasts the fire insulation out of the interstitial spaces between abutting wall panels, and allows the fire to spread through these spaces and into surrounding rooms. Thus, the weakened condition of conventional insulation that has been subjected to seismic activity is totally inadequate to withstand the blast of pressure from smoke and heated air that accompany a fire.
As a consequence, building shafts that have been faced with wallboard in a conventional manner and which have been subjected to seismic activity, allow a fire that reaches a shaft within as building to spread from floor to floor through the interstitial spaces between the abutting wallboard panels very rapidly. This greatly enhances the damage that a fire causes and significantly increases the peril of loss of life.
A principal object of the present invention is to provide an interior building shaft wall construction that provides an enduring fire barrier that will meet even the most stringent seismic and fire resistance code standards. Unlike conventional interior building shaft wall fabrications systems, the present invention does in fact meet the seismic resistance standards of current building code requirements and also the fire resistance standards demanded for interior building shafts. More specifically, the system of the present system allows wallboard panels to cycle vertically one inch up and down, toward and away from each other, and also 0.93 inches of cycling in lateral displacement relative to each other. Furthermore, following such seismic activity the interior building shaft wall construction system of the invention continues to meet applicable shaft wall fire resistance code standards.
The present invention provides a unique interconnection arrangement between the vertically abutting levels of interior building shaft walls.